Modeling of Bacillus cereus evolution in pasteurized cow milk locally distributedat point of sale: a case of three companies in Tlemcen region, Algeria

Bacillus cereus is among the most hazardous bacteria that could reduce the shelf life of pasteurized milk and could threaten consumers’ health. These bacteria groups are known for their heat resistance and their ability to produce two types of toxins, diarrheic and emetic. This study aimed to enumerate the B. cereus in raw cow’s milk collected from three companies in the Tlemcen region, then modeled, based on a probabilistic approach, their evolution throughout the process, split into six steps, until the point of sale. At first, the analysis of 242 samples on MYP medium, shows a high prevalence between 92% and 98% of B. cereus with variable concentrations among the three companies. Throughout the storage of milk at refrigeration temperatures (2°C, 4°C and 5°C), no growth of B. cereus was estimated. Otherwise, the pasteurization process reduces the contamination level depending on pasteurization temperature as for company A, the mean concentration decreases from 1.53 log CFU/mL to 1.07 log CFU/mL. In this study, the distribution step at ambient temperature changes significantly the B. cereus concentration to reach a critical concentration during July and August. In conclusion, the quality of raw cow milk must be controlled before reception on the farm and the cold chain must be maintained throughout all process points until consumption.